I believe that particular lamp used a (nominally) 3 volt "bicycle battery"
http://www.alfaquest.com/
Basically two cells 'stuck' together with one terminal at the front, that touched the back of the bulb directly, and t'other terminal on top that connected to the switch mechanism - the circuit was completed by 'connecting' this terminal through the switch to the body of the lamp.
I've seen similar lamps here that use two D cells and, at one point in the 1970s, Pifco made an adaptor http://www.alfaquest.com/
These JPEGs came from Paul Costin's excellent write-up at http://homepage.ntlworld.com/
Rear lamps usually used on D cell (which, IIRC, used to be called a U2 in Blighty) but there were some that were similar to the front lamps ...
Alan Lloyd
Schaumburg, Illinois, U.S.A.
> Today's Topics:
\r?\n> 7. Re: Hetchins lamps or lanterns, what is appropriate? (John Betmanis)
\r?\n>
\r?\n> Date: Sun, 16 Nov 2008 12:13:44 -0500
\r?\n> From: John Betmanis <johnb@oxford.net>
\r?\n> To: rapidfire10ring@hotmail.com,
\r?\n> Classicrendezvous@bikelist.org
\r?\n> Subject: Re: [CR]Hetchins lamps or lanterns, what is appropriate?
\r?\n> Message: 7
\r?\n>
\r?\n> The most common bicycle front light used by clubmen in the
\r?\n> UK in the 1950s was the Everready lamp you see on this bike:
\r?\n> http://www.classiclightweights.co.uk/
\r?\n> They used a flat 4.5 volt battery and also came in black.
\r?\n> I've seen chrome ones like it on eBay from time to time,
\r?\n> but I think those are newer.
\r?\n>
\r?\n> John Betmanis
\r?\n> Woodstock, Ontario
\r?\n> Canada